There is an energy supply circuit as a technique to continue a spark discharge for reducing a burden of a spark plug while suppressing unnecessary power consumption. The energy supply circuit is intended to continue a spark discharge that has occurred as a spark discharge (hereinafter, referred to as a main ignition) for an arbitrary period of time by supplying an electric energy to a negative side of a primary coil before the main ignition initiated by a so-called full-transistor type ignition circuit disappears, and applying a secondary current which flows in the same direction as the main ignition continuously.
It should be noted that in the following, a spark discharge to be continued by the energy supply circuit, that is, a spark discharge following a main ignition is referred to as a continuous spark discharge. In addition, a period in which the continuous spark discharge continues is referred to as a spark discharge duration.
The energy supply circuit maintains the spark discharge by adjusting the secondary current by controlling the primary current during the spark discharge duration. Further, by adjusting the secondary current during the continuous spark discharge, a burden of the spark plug is reduced and unnecessary power is suppressed from consuming, thus it is possible to continuous spark discharge.
Next, for purposes of understanding the present invention, a typical example of an energy supply circuit to which the present invention is not applied will be described with reference to FIG. 14.
An ignition device 100 shown in FIG. 14 includes a main ignition circuit 102 that generates a main ignition based on a full transistor to an ignition plug 101, and an energy supply circuit 103 that generates a continuous spark discharge by continuing the same polarity on the main ignition.
The main ignition circuit 102 causes a primary coil 106 to accumulate magnetic energy by passing a positive primary current from an on-vehicle battery 105 to the primary coil 106 by turning a switching element 104 on, then, by turning the switching element 104 off, causing a high voltage in the secondary coil 107 by converting the magnetic energy into an electrical energy using electromagnetic induction, thus causing the main ignition. Moreover, the energy supply circuit 103 accumulates a voltage of the on-vehicle battery 105 boosted by a booster circuit 108 in a capacitor 109, and the electrical energy accumulated in the capacitor 109 is supplied into a negative side of the primary coil 106 by turning on-off the switching element 110.
Furthermore, the ignition device 100 shown in FIG. 14 includes a feedback circuit 111 that detects the secondary current and feedbacks the secondary current to the energy supply circuit 103, and the feedback circuit 111 feedbacks the detected secondary current to a driver circuit of the energy supply circuit 103.
Here, in the feedback circuit 111, upper and lower thresholds for the secondary current is set, for example, and a feedback signal composed according to the comparison between a detection value and the upper and lower thresholds is outputted to the energy supply circuit 103.
In a case where the continuous spark discharge is continued by the energy supply circuit, it is preferable that an amount of the energy supplied is controllable in accordance with an operating condition of an engine. In other words, when a gas flow rate is high in a cylinder (at the time the engine is running at high speed), it is necessary to supply a large amount of energy in a short period of time for the continuous discharge, and when the gas flow rate is low in the cylinder (at the time the engine is running at low speed), it is preferable to supply only a small amount of energy over a long period of time for increasing ignition opportunities. Therefore, when it is impossible to control the energy supplying amount, there is a possibility that not enough energy will be available when it is necessary to supply the high energy in a short period of time, or the power consumption may become unnecessarily large when it is preferable to supply the low energy over a long period of time, for example.
It should be noted that in a conventional ignition device without an energy supply circuit, a multiple discharge repeatedly generating the main ignition based on the full transistor by a circuit equivalent to the main ignition circuit as a technique to continuous spark discharge is known. Then, the conventional ignition device that performs the multiple discharge controls energization of the primary coil based on control signals (ignition signal IGt and discharge continuation signal IGw) given from an ECU (abbreviation of Engine Control Unit) that constitutes a core of an engine control. Here, the ignition signal IGt is a signal for controlling a start time of the multiple discharges, and the discharge continuation signal IGw is a signal for controlling the duration of the multiple discharge (refer to Patent Documents 1 and 2, for example).
However, when supplying the energy by the energy supply circuit as described above, and when the ignition signal IGt and the discharge continuation signal IGw similar to the conventional technology are used, although it is possible to control a supplying period of the energy by the discharge continuation signal IGw, it is impossible to control a supplied amount of the energy. Therefore, there is a possibility that the amount of energy becomes short when it is necessary to supply the high energy in a short period of time, or the power consumption may become unnecessarily large when supplying the low energy over a long period of time.